Natural and synthetic porous materials and media are widely used as substrates in various articles and processes. Porous materials may include macroporous, mesoporous, microporous, or nanoporous materials, or combinations thereof. Porous materials may include metals, oxides, polymers, or other materials. Porous materials may be manufactured using casting, infiltration, foaming, deposition, drying, or supercritical drying. Depending on the application, porous materials may be pre-treated or further treated using thermal, chemical, acoustic, electrical, or other treatments.
Functionalized porous materials may be used in a wide variety of applications, For example, functionalized porous material, such as functionalized porous silica, may be used in applications including sensors, catalysts, heavy metal recovery, and drug delivery. Materials such as aminomethyl-anthracene functionalized, templated porous silica may be used for sensing ATP by fluorescence quenching. Materials such as thiol-functionalized, templated porous silica may be used for heavy metal ion recovery. Porous materials may be used for catalysis, for instance, silica based catalyst supports including W-peroxo compounds for epoxidation, Grubb's catalyst for metathesis (double replacement reaction) and allylic amination. Controlled release by chemical reduction of disulfide linkage between CdS and porous silica may be used for drug delivery via CdS nanoparticles.
Known techniques for such functionalization are performed using a synthetic grafting approach of porous oxides with pore sizes tailored for the particular target application. Some porous oxide surfaces may not be amenable to direct functionalization, and therefore some techniques for functionalization of porous substrates may include an intermediate hydroxylation step to introduce hydroxyl groups on surfaces, which can subsequently be functionalized with functional groups. However, in known techniques that employ hydroxylation as an intermediate step, the functionalization step functionalizes all available hydroxyl groups. Therefore, all hydroxylated surfaces may get functionalized.
Conventional techniques of functionalizing may result in nonselective functionalization of pores, where pores are randomly functionalized with functional groups irrespective of their pore size. FIG. 1 is a conceptual diagram presenting a lateral cross-sectional view of a structure including a porous material exhibiting a broad pore size distribution, functionalized by existing nonselective techniques. Porous substrate 120 includes a plurality of pores 140. The plurality of pores 140 includes a first plurality of pores 140a having a first average pore size, a second plurality of pores 140b having a second average pore size, and a third plurality of pores 140c having a third average pore size. In examples, the first average pore size is smaller than the second average pore size, and the second average pore size is smaller than the third average pore size. Nonselective techniques of functionalizing porous substrate 120 with different functional groups, for instance, a first functional group A, a second functional group B, and a third functional group C, typically result in nonuniform and nonselective functionalization of pores that is not correlated with the average pore size. This may result from a failure of conventional techniques to selectively hydroxylate pores depending on their pore sizes, whereby a subsequent functionalization of the hydroxylated pores results in nonselective functionalization. For example, each of the first plurality of pores 140a, the second plurality of pores 140b, and the third plurality of pores 140c, may be hydroxylated and functionalized, or directly functionalized by either of functional groups A, B, or C, regardless of the average pore size of the respective plurality of pores, ultimately resulting in a nonselectively functionalized substrate, as shown in FIG. 1.